ASTM_F_2358_-_04.pdf

Designation:F 2358 04Standard Guide forMeasuring Characteristics of Sapphire Substrates1This standard is issued under the fixed designation F 2358;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This guide covers a nondestructive procedure to deter-mine the form of clean,dry sapphire substrates.1.2 This guide is applicable to substrates 25 mm or larger indiameter,with a minimum thickness of 100 m.This guide isindependent of surface finish.1.3 The measurements described in this guide may beapplied to the entire global surface of the substrate,or tosmaller localized areas.1.4 The value of the measurements described in this guidewill be affected by the amount of edge exclusion(that is,thearea around the perimeter of the part which is ignored).Theamount excluded should be agreed upon by the producer andconsumer using this standard.1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory requirements prior to use.2.Referenced Documents2.1SEMI Standard:2M3 Specifications for Polished Monocrystalline SapphireSubstrates3.Terminology3.1 General Definitions:3.1.1 back surfacethe surface opposite the front surface.If there is no difference between the front and back surfaces,then the surfaces may be determined arbitrarily,and aretherefore interchangeable.3.1.2 best-fit planethe theoretical plane established byusing the least squares fit method,based on data obtained fromthe quality area only.3.1.3 best-fit spherethe theoretical sphere established byusing the least squares fit method,based on data obtained fromthe quality area only.3.1.4 front surfacethe preferred surface,as defined by theuser.3.1.5 quality areathe central area of a wafer surface,defined by a nominal edge exclusion,over which the specifiedvalues of a parameter apply.If the quality area is not circular,the“circle defining the quality area”shall be defined as theminimum diameter circle which contains all of the data withinthe quality area.3.1.6 reference planethe plane from which deviations aremeasured.3.1.7 restrained conditionthis refers to the state of thesubstrate under test,when one side of the substrate is clampedto an ideally flat surface;for example,when pulled down by avacuum onto an ideally clean flat chuck.3.1.8 sapphire substrategeneric term for any flat wafer,window,wafer carrier,or substrate made of sapphire material.These terms may be used interchangeably in this standard.3.1.9 thicknessthe distance through the substrate betweencorresponding points on the front and back surfaces.3.1.10 unrestrained conditionthis refers to the state of thesubstrate under test,when the substrate is in a stress-freecondition with minimal deformation due to gravity.3.2 Definitions of Unrestrained Parameters:3.2.1 sagthe distance from the apex of the best-fit sphereto a plane intersecting the sphere in a circle with a diameterequal to the diameter of the circle defining the quality area,measured in an unclamped condition.This value will bepositive(+)if the measured surface is convex,and negative()if the surface is concave.See Fig.1.3.2.2 sorithe maximum distance above,plus the maxi-mum distance below the front surface best-fit plane of a free,unclamped substrate.See Fig.2.3.3 Definitions of Restrained Parameters(see Note 1):3.3.1 front-to-front deviation(FFD)the maximum dis-tance above,plus the maximum distance below the frontsurface best-fit plane of a substrate,measured with the backsurface restrained.See Fig.3.3.3.2 taperthe linear component of the variation in thick-ness across a substrate,indicated by the angle between thebest-fit plane to the front surface and the ideally flat backsurface of the substrate.See Fig.4.1This guide is under the jurisdiction of ASTM Committee F01 on Electronicsand is the direct responsibility of Subcommittee F01.15 on Compound Semicon-ductors.Current edition approved May 1,2004.Published June 2004.2Available from Semiconductor Equipment and Materials International(SEMI),3081 Zanker Rd.,San Jose,CA 95134.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.3.3.3 total thickness variation(TTV)the difference be-tween the maximum and minimum values of the thickness ofthe substrate.See Fig.5.NOTE1Even though the above parameters define the variation of atheoretically restrained substrate,the measurements may be performed inthe unrestrained state,with calculations performed to simulate therestrained condition.4.Summary of Guide4.1 The surfaces of samples under test may be measuredusing optics,interferometry,or any other technique